Reversible Addition Fragmentation Chain Transfer Polymerization (RAFT) Of Methyl Methacrylate(MMA) In Emulsion

Reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the living/controlled free radical polymerization techniques. Compared with other living/controlled free radical polymerization methods, major advantages of the RAFT polymerization are i) very similar recipe and processes to the traditional free radical polymerization, ii) a larger variety of monomers, and iii) higher polymerization rate.In the past decade, RAFT polymerization has been extensively investigated in bulk and solution polymerization. More recently, the research attention of the RAFT processes has been directed to emulsion/miniemulsion polymerization systems, which are commercially viable methods for implementing RAFT polymerization and environmentally benign. However, few successes of RAFT polymerization have been reported for an ab initio emulsion system. The colloidal instability is the major problem. An oily layer or very large particle size were usually observed. Poor control in molecular weigh and polydispersity index were also reported in most cases. The current thesis aims at revealing the mechanism of colloidal instability in an ab initio emulsion RAFT polymerization.Based on the theoretical simulations, we assume the superswelling occurring in Stage I of RAFT emulsion polymerization is the cause for the colloidal instability. Theoretical analysis predicts that stability of the emulsion polymerization could be improved by increasing initiation rate, surfactant level, and targeted molecular weight. The RAFT polymerization of MMA in emulsion was then experimentally investigated in order to check the predictions. The experimental results are in excellent accord with the theoretical predictions. The poor control in molecular weight and polydispersity index were found to be significantly dependent on the colloidal instability. For the first time, we demonstrated that RAFT polymerization can be successfully implemented with little coagulum, well control in molecular weight, and low polydispersity index using the same process as the traditional emulsion polymerization but with higher the surfactant levels and initiation rates.By measuring the concentration of RAFT agents in the droplets in the early stage of the emulsion polymerization, it is evident that there is no limitation of mass transportation for RAFT agents to cross the water phase from droplets to particles. Mass transportation limitation is less likely to be the reason of the colloidal instability.The RAFT polymerization of styrene in emulsion is still colloidally unstable even with higher initiation rate and surfactant concentration. The semibatch of the RAFT polymerization of MMA in emulsion to decrease the surfactant concentration broadens the molecular weight distribution. Further investigations are needy.